This invention relates to a liquid dispensing and vapor recovery system and control unit used therein and, more particularly, to such a system and unit in which liquid is dispensed from a storage tank to a receptacle while vapors from the receptacle are passed to the storage tank.
With the increased emphasis on preventing pollution of the atmosphere, recent attention has been directed to minimizing the introduction of gasoline vapors into the atmosphere from both permanent type underground storage tanks for the gasoline, and from the vehicles into which the gasoline is ultimately dispensed.
Gasoline vapors can easily be recovered from underground storage tanks by providing a separate vapor return line which connects the storage tank to the transport truck which periodically fills the tank. In this manner, the gasoline introduced into the tank from the transport truck will displace the vapors and force them through the vapor recovery line to the truck whereby they are ultimately disposed of either by burning or through compression - refrigeration systems.
However, it has been extremely difficult to devise a satisfactory vapor recovery system from the gasoline tanks of vehicles. For example, previous proposals have utilized what is commonly referred to as a balanced displacement system in which the gasoline entering the tank forces the vapors through a separate line to the storage tank. However, this system has been less than satisfactory for several reasons. For example, since the fluid in the vehicle tank becomes pressurized upon introduction of the gasoline, any type of leak in the interface between the dispensing nozzle and the vehicle tank, such as that caused by an improper seal between the nozzle and the tank, results in a leakage of the gasoline vapors into the atmosphere.
Although it has been suggested to use a vacuum pump or a blower to remove the vapors from the vehicle tanks, this type of installation is disadvantageous from several standpoints. For example, the pump or blower is relatively expensive and creates potential safety problems due to the fact that it is electrically operated. Also, the output from the pump or blower is passed directly into the storage tank which pressurizes the tank and therefore increases vapor losses from the tank through its vent pipe.
In copending U.S. patent application Ser. No. 400,555, filed by Kirk Fowler and Elmer M. Deters on Sept. 25, 1973, and assigned to the same assignee of the present invention, a gasoline dispensing and vapor recovery system is disclosed which overcomes the above-mentioned problems by providing an injector for establishing a reduced pressure zone in response to fluid flow from the storage tank to the vehicle receptacle, with the reduced pressure zone functioning to draw the vapors from the receptacle back to the tank. Although this design has proven to be satisfactory, it has a limited operational range and is therefore not readily adaptable to dispensing installations of varying capacity.